The invention relates to a method of extinguishing the unwanted arc formed in a switch during circuit-breaking, using a magnetic field by means of which the arc is lengthened until it is extinguished.
When opening an electric switch, a problem is encountered in that an electric arc forms on separation of the switch contacts, prevents interruption of the circuit, and causes destruction of the switch contacts. Attempts have therefore been made, using various aids, to prevent the formation of such an arc or at least to allow rapid extinction of the arc.
It is known for this purpose to introduce extinguishing gases into the switch housing, but this has the disadvantage that the structural design of such a switch is very complicated since the switch chamber must be sealed gas-tight from the environment.
Another method of extinguishing the arc involves generating a magnetic field in the region of the switch contacts. The arc normally moves in this magnetic field under the influence of the Lorentz force. If the switch contacts are formed in such a way that the distance between the contacts increases in the direction of movement of the arc under the influence of the Lorentz force by using, for example, switch contacts which are curved away from each other, then the electrical arc will become progressively longer during the displacement under the influence of the magnetic forces until it finally breaks. This operation is called magnetic blow-out. Although this method operates well in itself, it takes a relatively long time for the electric arc to achieve the length needed to break, i.e. the extinction of the arc does not take place quickly enough in many cases.